GB1130391A - Improvements relating to heat exchangers - Google Patents

Abstract

1,130,391. Forced flow steam generators. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 21 Dec., 1965 [4 Jan., 1965], No. 242/65. Heading F4A. A sub-critical forced recirculation steam generating installation, heated by a liquid metal such as sodium or sodium/potassium comprises evaporating, superheating and reheating sections 10, 11, 12 respectively in the form of shell and tube heat exchangers. Liquid metal from inlets 13 and 14 flows in parallel through the superheater 11 and reheater 12, in each case in three passes, and then flows through ducts 15 and 16 into evaporating section 10, wherefrom after three passes it leaves through outlet 27. Feed water from inlet 29 is sprayed into drum 20, from where it is fed to the evaporating section 10 through downcomer 21, centrifugal pumps 22 and 23 mounted in parallel, and inlet riser 26. Steam from evaporating section 10 then returns to drum 20 through an outlet riser (not shown) and manifold 28. Steam from the drum 20 is led through manifold 30 and pipe 31 to the superheating section 11, the superheated steam outlets being shown as 32. The reheater inlet and outlet pipes are shown as 33, and 34 respectively. The construction of the reheating section 12 is in other respects identical to that of superheating section 11. This, Fig. 3, comprises a shell containing an extension 36 of entry duct 13 and an annular double-walled hollow baffle 38 sealed to the top of the superheater shell to define three passes for the liquid metal. The liquid metal from inlet 13 flows upwardly through duct 36, through lateral ports 37 into the annular down pass, filled with liquid metal to a level indicated 40, then around the bottom of baffle 38 and up the external annular pass filled with liquid metal to a level indicated 41, to pass to the collector annulus 39 and outlet duct 15. Steam from pipe 31 is superheated in a spiral coil of U- tubes 58 extending between toroidal inlet and outlet headers 56, 57 respectively above the third and second liquid metal passes respectively. The space between the toroidal headers and the liquid metal levels 40, 41 is filled with nitrogen from gas inlets 43, 44 respectively, which incorporate isolating valves, so that the spaces which are sealed from one another may be maintained at different pressures to control the liquid level in the passes. In this way contact between the liquid metal and the welds connecting the tubes 58 to the headers 56, 57 is avoided. The superheating section 11 is also provided with an excess pressure relief rupture disc 60 in pipe 59, a normally closed liquid metal drain pipe 61, metal level detectors 63 for the various passes and U-tube spacer grids 64. The evaporating section (10, Fig. 4, not shown), is generally similar to superheater 11 but is formed with three liquid metal passes between an annular inlet (35) and central outlet (27), and has U- shaped steam generating tubes (64) extending between annular headers (65, 66) at the top of the first and second liquid metal passes respectively. In all cases the tubes may be of a double-wall construction, the interspace being filled with lead to reduce the likelihood of contact on leakage between the liquid metal and water, or steam.